Pillbox antenna



y 1953\ LAN JEN CHU EI'AL 2,633,545

PILLBOX ANTENNA Filed March 14, 1946 FIG.I

FIG. 2

' INVENTOR. MARION A. TAGGART LAN JEN CHU ATTORNEY Patented May 12, 1953 .PILLBOX ANTENNA Lan Jen Chu, Brookline, Mass., and Marion A. Taggart, Indianapolis, Ind., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy ApplicationMarch 14, 1946, Serial No. 654,493

Claims.

1 This invention relates to an antenna, and more particularly to a pillbox antenna having two layers so arranged that the feed and radiating apertures do not obstruct each other.

Line sources of electromagnetic energy combined with cylindrical reflectors have found con-' siderable use in microwave antenna design. The pillbox, a short length of parabolic cylinder connecting two parallel plates, is one type of line source which has been used extensively, despite some serious disadvantages.

There are two major disadvantages in the use of a conventional pillbox in an antenna system. First, the pillbox feed, by obstructing th aperture, lowers the power gain and increases the. intensity of secondary lobes in the radiation pattern of the antenna. Second, energy reflected into the feed from the parabolic back plate of the pillbox makes broad-banding, or impedance matching over a broad frequency band, impossible without the incorporation of a compensating device, which causes further degeneration of the pattern.

It is an object of this invention improved pillbox antenna.

It is another object of this invention to provide to provide an a pillbox antenna having an aperture free from obstructions.

It-is' a further object of this invention to pro-, vide a pillbox antenna which is properly matched in impedance to a feed over a broad frequency band.

It is still another object to provide a pillbox antenna having two separated sections, one above' the other coupled by a toroidal bend, with the feed in one section and the aperture in the other. These and other objects will be more apparent upon consideration of the following description,

together with the accompanying drawings, in which:

Fig. 1 is a cutaway perspective view'of an embodiment of this invention; and, a

Fig; 2 is a sectional view along line IIII of Fig. 1. a

Referring to the drawings, a conducting parabolic reflector l3, comprising a short section of parabolic cylinder, is closed at its ends by conducting top and bottom plates 20 and 2|, respec-' tively. An intermediate conducting plate I'l, having a parabolic edge conforming to thecurvature of parabolic reflector I3, is fixed midway between plates 20 and 2|, forming a septum, with a uniform separation being maintained between the parabolic edge of plate I! and parabolic reflector l3.

Plates ii and 2! are extended beyond the focus of parabolic reflector l3 and are flared to form an aperture. Top and bottom plates 20 and 2| and septum plate ii are fastened to end plates l4 and I5, which form the end boundaries of I the aperture.

A feed, comprisingthe open end of a wave guide transmission line 10,. is positioned at the. focus of reflector l3 and is terminated between" The aperture formed by plates l1 and 20 is closed by'conducting strip Iii except plates l1 and 20.

at the center, where the feed is introduced.

It can be seen easily that the electromagnetic energy introduced into the pillbox by the eed will be propagated through the space between plates I! and 20 and will be coupled to the space between plates I1 and 2| throughthe'ppening' between parabolic reflector l3 and the parabolic edge of plate IT. The energy reflected by parabolic reflector l3 will be propagated through the space between plates I! and 2|, arriving at the flared aperture with a uniform phasejfront. It

will be noted that the radiating aperture is free, from obstruction by the feed as is the case in. the conventional pillbox. By reciprocity, the pillbox will produce equally satisfactory results when used for either transmitting or receiving electromagnetic energy.

Since certain changes may be made in the above described antenna anddifferent embodiments of the invention could be made without,

departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

bolic edge being uniformly separated from said parabolic reflector, a conductive strip lying in a plane through the focal line of said parabolic] cylinder'separating said first and said ilfiterrnef f diate' conductive plates, and a transmissionline coupled through said conductive strip to said parabolic reflector between said first and said intermediate conductive plates, said second and said intermediate plates being flared outwardly.

2. A pillbox antenna comprising, a short parabolic reflecting cylinder axially terminated in first of said cylinder as to form an opening for transferring energybetween the sectionsgof said para-mbolic cylinder.

3. A pillbox antenna comprising, a short parabolic reflecting cylinder axially terminated in first and second flat conductive plates, andpan intermediate conductive plate centrally disposed between said first and secondplates and., lying in a plane substantially parallel to theplanes-of said first and second plates, said intermediate...

said unobstructed line source of energy.

plate having a substantially parabolic edge conforming to the curvature of said parabolic reflecting cylinder, said parabolic edge being uni:

formly separated from saidparabolic cylinder.

4. A pillbox antenna comprising, ,a short parabolic reflecting cylinder axially terminated-in first and. second parallel conductive plates, an-

reflecting cylinder axially 'terminatedin firstv andsecond conductive plates, a .thirdconductive.

plate disposed perpendicular, to and bisecting the focal line of said, reflecting cylinder, saidthird conductingjplate dividing saidreflecting cylinder.

into two substantially similar reflecting cylinders andbeing sodisposed adjacent .the parabolic.sur-.

face of. said cylinder as to form an opening for permitting the reflection .of energy fromoneto the other of said two reflectors, and separate energytransfer means coupled. to each .of said reflectors, said energy transfer. means beingsubstantially completely. isolatedv one from ,the other...

6. A pillbox antenna comprising aparabolic reflectingv cylinder axially .terminateddn first and second conductive plates, a third conductive.-

plate disposed perpendicular to and bisectingthe;

focal line of said reflecting cylinder, said third conducting plate dividing saidreflecting-cylinder int two substantially similar reflecting cylinders and, being so disposed relative to the reflecting.

cylinderas to form an opening-forpermitting transfenof energy between said two reflectors, a wave, guide. connected to one of said reflectors substantially atthe focal line thereof and a flared horn formed at the extremities of the other of said two reflectors- 7. A pillbox antennacomprisingaa, parabolic reflecting cylinder axially terminated infirst and second flat conductive plates, .an intermediate I plate parallel. to said first and second plates and equally spaced therefrom by an amount less than a half wave length at the frequency of operation 4 of said antenna, said intermediate plate dividing said cylinder into two sections and being so disposed adjacent the parabolic surface of said cylinder as to form an opening between the sections of said parabolic cylinder.

8. A pillbox antenna for providing an unobstructed linesource of energy comprising, a parabolicjrefiecting cylinder axially terminated in first and second plates, an intermediate plate parallel to said first and second plates and dividing said reflecting cylinder into two substantially similara-reflectors, said intermediate plate being uniformly spaced from said reflecting cylinder, transmission means'coupled to one of said refiectors, and energy. interchange means at the mouthof the other of said reflectors for providing 9. A pillbox antenna comprising a parabolic reflecting. cylinder axially terminated in first and second substantially parallel, flat conductive plates, an intermediate conductive plate perpen.-. dicular to and bisecting the focal 'line of said reflecting cylinder, said intermediate plate having a substantially parabolic edge within said reflecting cylinder and conforming to the curva-. ture'thereof, said parabolic edgebeing uniformly spaced from said reflecting-cylinder, a conductive strip lying in a'plane' through the focal line of said reflecting cylinder, and transmission means coupled through said conductive'strip to theportion 'of said reflecting cylinder lying between said first and intermediateplates.

10. A pillbox antenna; comprising a parabolic. reflecting cylinder axially terminated in first. and

second substantially parallel conductive plates, an

intermediate conductive plate perpendicular to and bisecting the focal line of said reflectingv cylinder, said intermediate plate havinga sub stantially parabolic .edge Within saidrefiecting. cylinder and conforming to the curvature thereon. said parabolic edge being uniformlyspacedfrom. said parabolic reflectingcylinder, a conductive" strip disposed in a plane including thatv portion of the focal lineof said. parabolic reflector-includedbetween said first andsaidintermediate conductive. plates, said conductive strip having an opening formed therein, .a wave guide terminated by said intermediate plate and havingalateral openingin. register with saidopening insaid con-v ductive strip, said registered openingsqbeingt centered, on the focal line of. said reflectonsaid. second and intermediate plates extending out.-.- wardly beyond. said .flrst. concluctiveplate and being flared atthe extremities thereof to forman electromagnetic horn.

LAN JEN' CHU. 1 MARION A; TAGGARTH- 1 References Cited in the file of thispatent '1 UNITED STATES. PATENTS Number Name 7 Dates.

2,223,224? Newhouse Nov. 26, 1940 2,283,935 King May 26, 1942 3 2,398,095 5 Katzin Apr. 9, 1946. 2,405,242 Southworth Aug. 6, 1946 2,407,068 Fisk-e et-al. Sept. 3, 1946 2,435,408 Tawney? F eb. 24, 1948 2,452,2.02 Lindenblad Oct. 26, 1948:" 2,479,673.. Devore Aug; 23, 1949- 

